Detection of Eastern Equine Encephalomyelitis Viral Antigen in Avian Blood by Enzyme Immunoassay: a Laboratory Study

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Abstract
An enzyme immunoassay (EIA) was evaluated for its efficacy at detecting eastern equine encephalomyelitis (EEE) virus in avian blood and brain specimens. Preliminary analysis of blood from experimentally infected house sparrows and naturally infected whooping cranes showed that EEE antigen could be detected with the EIA. Polyclonal mouse antibodies were selected for antigen capture, and rabbit antibodies were selected for antigen detection. Overnight antigen incubation increased sensitivity. The lower limit of EEE antigen detection was 103.5 TCID50/ml for a stock of virus. Sensitivity was 10% (2/20) for antigen detection in the blood of chicks inoculated with EEE virus <24 hr earlier. At 24 and 48 hr after infection, sensitivity was 100% (10/10). Sensitivity and specificity of antigen detection were excellent (100% for both) in house sparrows experimentally inoculated with EEE, Highlands J (HJ), western equine encephalomyelitis (WEE), or St. Louis encephalitis (SLE) virus and bled at 24 hr intervals. Cross-reactivity was observed, however, with high concentrations (105.5 TCID50/ml) of HJ virus. EEE antigen was detected in avian blood by the EIA after infectious virus had declined to undetectable levels. The EIA is a useful alternative to virus isolation in cell culture for diagnosis or detection of EEE virus infections in birds. The test has the advantages of being simple, rapid, and capable of detecting antigen in the absence of infectious virus.